Capacitive touch system using frequency division multiplexing and operating method thereof

ABSTRACT

A capacitive touch system including a drive end, a capacitive touch sensing device and a detection end is provided. The drive end inputs a modulated drive signal into an input channel of the capacitive sensing device, wherein the modulated drive signal includes a plurality of driving frequencies. The detection end detects a detection signal of an output channel of the capacitive sensing device and generates a two-dimensional detection vector corresponding to each of the driving frequencies.

BACKGROUND

1. Field of the Disclosure

This disclosure generally relates to a touch system and, moreparticularly, to a capacitive touch system using frequency divisionmultiplexing and an operating method thereof.

2. Description of the Related Art

Capacitive sensors generally include a pair of electrodes configured tosense a conductor. When the conductor is present, the amount of chargetransfer between the pair of electrodes can be changed so that it isable to detect whether the conductor is present or not according to avoltage variation. It is able to form a sensing matrix by arranging aplurality of electrode pairs in a matrix.

FIGS. 1A and 1B are schematic diagrams of a conventional capacitivesensor which includes a first electrode 91, a second electrode 92, adrive circuit 93 and a detection circuit 94. The drive circuit 93 isconfigured to input a drive signal X to the first electrode 91. Electricfield can be generated between the first electrode 91 and the secondelectrode 92 so as to transfer charges to the second electrode 92. Thedetection circuit 94 is configured to detect the amount of chargetransfer Y to the second electrode 92. The electric field is representedby, for example, a capacitor.

When a conductor is present, e.g. shown by an equivalent circuit 8, theconductor can disturb the electric field between the first electrode 91and the second electrode 92 so that the amount of charge transfer Y′ isreduced. The detection circuit 94 can detect a voltage variation toaccordingly identify the presence of the conductor.

As the capacitive sensor is generally applied to various electronicdevices, e.g. the liquid crystal display (LCD), the voltage variationdetected by the detection circuit 94 can be interfered by noises of theelectronic devices to degrade the detection accuracy.

Accordingly, it is necessary to provide a way to solve the aboveproblem.

SUMMARY

The present disclosure provides a capacitive touch system and anoperating method thereof that input a mixed signal containing aplurality of driving frequencies into each input channel to achieve theobject of reducing the noise interference, power consumption anddetection interval, wherein the mixing signal is generated by modulatinga drive signal using, for example, frequency division multiplexing ororthogonal frequency division multiplexing.

The present disclosure provides a capacitive touch system including adrive circuit, a capacitive sensing matrix, an encoding module, amodulation module, a detection circuit and a decoding module. The drivecircuit is configured to output a drive signal. The capacitive sensingmatrix includes a plurality of sensing elements arranged in rows andcolumns. The encoding module is configured to encode the drive signalcorresponding to each row of the sensing elements to output a pluralityof encoded drive signals. The modulation module is configured tomodulate the encoded drive signals using frequency division multiplexingand concurrently output a plurality of encoded and modulated drivesignals to each row of the sensing elements, wherein each of the encodedand modulated drive signals contains a plurality of driving frequencies.The detection circuit is coupled to the capacitive sensing matrix andconfigured to respectively generate a detection matrix corresponding toeach of the driving frequencies according to a detection signal of eachcolumn of the sensing elements. The decoding module is configured todecode the detection matrices to output a plurality of two-dimensionaldetection vectors corresponding to each of the sensing elements, whereinthe two-dimensional detection vectors associated with each of thesensing elements respectively correspond to the driving frequencies.

The present disclosure further provides a capacitive touch systemincluding a drive circuit, a capacitive sensing matrix, a modulationmodule and a detection circuit. The drive circuit is configured tooutput a drive signal. The capacitive sensing matrix includes aplurality of sensing elements arranged in rows and columns. Themodulation module is configured to modulate the drive signal usingfrequency division multiplexing to respectively output a modulated drivesignal to each row of the sensing elements, wherein the modulated drivesignal contains a plurality of driving frequencies. The detectioncircuit is coupled to the capacitive sensing matrix and configured torespectively generate a two-dimensional detection vector correspondingto each of the driving frequencies according to a detection signal ofeach column of the sensing elements.

The present disclosure further provides an operating method of acapacitive touch system. The capacitive touch system includes acapacitive sensing matrix which has a plurality of drive electrodes anda plurality of receiving electrodes. The operating method includes thesteps of: concurrently inputting encoded and modulated drive signals tothe drive electrodes in each drive time slot of a plurality of drivetime slots of a frame period of the capacitive sensing matrix, whereinthe encoded and modulated drive signals are modulated by frequencydivision multiplexing to contain a plurality of driving frequencies;sequentially detecting the receiving electrodes of the capacitivesensing matrix within the frame period to generate a plurality ofdetection matrices corresponding to each of the receiving electrodes,wherein the detection matrices associated with each of the receivingelectrodes respectively correspond to the driving frequencies; anddecoding the detection matrices to generate a plurality oftwo-dimensional detection vectors corresponding to each of the drivingfrequencies of each of the receiving electrodes.

The present disclosure provides a capacitive touch system including adrive circuit, a capacitive touch sensing device, a modulation moduleand a detection circuit. The drive circuit is configured to output adrive signal. The capacitive touch sensing device includes at least onesensing element. The modulation module is configured to modulate thedrive signal using frequency division multiplexing and output amodulated drive signal to the at least one sensing element, wherein themodulated drive signal contains a plurality of driving frequencies. Thedetection circuit is coupled to the capacitive touch sensing device andconfigured to respectively generate a two-dimensional detection vectorcorresponding to each of the driving frequencies according to adetection signal of the at least one sensing element.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosurewill become more apparent from the following detailed description whentaken in conjunction with the accompanying drawings.

FIGS. 1A-1B are schematic diagrams of a conventional capacitive sensor.

FIG. 2 is a schematic block diagram of a capacitive touch sensing deviceaccording to one embodiment of the present disclosure.

FIGS. 3A-3B are schematic block diagrams of a capacitive touch sensingdevice according to some embodiments of the present disclosure.

FIG. 4 is a schematic diagram of a norm of vector and a thresholdaccording to one embodiment of the present disclosure.

FIG. 5 is a schematic diagram of a capacitive touch system according toone embodiment of the present disclosure.

FIG. 6 is a schematic diagram of drive signals of every channel in everydrive time slot of a concurrent driving capacitive touch systemaccording to a first embodiment of the present disclosure.

FIG. 7 is a schematic diagram of a concurrent driving capacitive touchsystem according to a first embodiment of the present disclosure.

FIG. 8 is a schematic block diagram of a drive end of a capacitive touchsystem according to a second embodiment of the present disclosure.

FIG. 9 is a schematic block diagram of a detection end of a capacitivetouch system according to a second embodiment of the present disclosure.

FIG. 10 is a schematic diagram of modulated drive signals according tosome embodiments of the present disclosure.

FIG. 11 is a flow chart of an operating method of a capacitive touchsystem according to a second embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

Referring to FIG. 2, it is a schematic block diagram of a capacitivetouch sensing device according to one embodiment of the presentdisclosure. The capacitive touch sensing device of this embodimentincludes a sensing element 10, a drive circuit 12, a detection circuit13 and a processor 14. The capacitive touch sensing device is configuredto detect whether an object (e.g. a finger, water drop or metal plate,but not limited to) approaches the sensing element 10 according to achange of the amount of charges on the sensing element 10. Ways todetect whether the object approaches the sensing element 10 are wellknown and not limited to the above method.

The sensing element 10 includes a first electrode 101 (e.g. a driveelectrode) and a second electrode 102 (e.g. a receiving electrode), andan electric field can be produced to form a coupling capacitance 103between the first electrode 101 and the second electrode 102 when avoltage signal is provided to the first electrode 101. The firstelectrode 101 and the second electrode 102 are arranged properly withoutparticular limitations as long as the coupling capacitance 103 is formed(e.g., via a dielectric layer therebetween), wherein principles offorming the electric field and the coupling capacitance 103 between thefirst electrode 101 and the second electrode 102 are well known and thusare not described herein.

The drive circuit 12 is, for example, a signal generator which providesa drive signal X(t) to the first electrode 101 of the sensing element10. The drive signal X(t) is, for example, a time-varying signal such asa periodic signal. In other embodiments, the drive signal X(t) is, forexample, a pulse signal such as a square wave or a triangle wave, butnot limited thereto. The drive signal X(t) couples a detection signaly(t) on the second electrode 102 of the sensing element 10 through thecoupling capacitance 103.

The detection circuit 13 is coupled to the second electrode 102 of thesensing element 10 and configured to receive the detection signal y(t).The detection circuit 13 modulates (or mixes) the detection signal y(t)respectively with two mixing signals so as to generate a pair ofmodulated detection signals, which are configured as two components of atwo-dimensional detection vector (I,Q) after the integration,downconversion and/or filtering. The two mixing signals are, forexample, continuous signals or vectors that are orthogonal ornon-orthogonal to each other. In one aspect, the two mixing signalsinclude a sine signal and a cosine signal.

The processor 14 is configured to calculate a scale of the pair ofmodulated detection signals, which is configured as a norm of vector ofthe two-dimensional detection vector (I,Q), and compare the norm ofvector with at least one threshold TH so as to identify a touch event.In one aspect, the processor 14 calculates the norm of vector R=√{squareroot over (I²+Q²)} by software. In other aspects, the processor 14calculates by hardware or firmware, such as using a CORDIC (coordinaterotation digital computer) shown in FIG. 4 to obtain the norm of vectorR=√{square root over (I²+Q²)}, wherein the CORDIC is a fast algorithm.The processor 14 is, for example, a microprocessor (MCU), a centralprocessing unit (CPU) or an application specific integrated circuit(ASIC).

In FIG. 4, when there is no object close to the sensing element 10, anorm of vector calculated by the processor 14 is assumed to be R; andwhen an object is present nearby the sensing element 10, the norm ofvector is decreased to R′. When the norm of vector R′ is smaller than athreshold TH, the processor 14 identifies that the object is presentclose to the sensing element 10 to induce a touch event. It should bementioned that when another object, such as a metal plate, approachesthe sensing element 10, the norm of vector R can be increased.Therefore, it is possible for the processor 14 to identify a touch eventwhen the norm of vector exceeds another predetermined threshold. In someembodiments, the processor 14 compares a variation of the norm of vector(e.g., a difference value between the norm of vectors R′ and R in FIG.4) with a variation threshold to accordingly identify a touch eventinstead of comparing a value of the norm of vector with a predeterminedthreshold.

FIGS. 3A and 3B are schematic diagrams of a capacitive touch sensingdevice according to some embodiments of the present disclosure in whichdifferent implementations of the detection circuit 13 are shown.

In FIG. 3A, the detection circuit 13 includes an analog-to-digitalconverter (ADC) 133, two mixers 131 and 131′, and two integrators 132and 132′, and is configured to process a detection signal y(t) togenerate a two-dimensional detection vector (I,Q). The ADC 133 isconfigured to convert the detection signal y(t) to a digital detectionsignal y_(d)(t). The two mixers 131 and 131′ are configured to modulate(or mix) the digital detection signal y_(d)(t) with two mixing signals,such as MX₁=√{square root over (2/T)} cos(ωt) and MX₂=√{square root over(2/T)} sin(ωt) herein, so as to generate a pair of modulated detectionsignals y₁(t) and y₂(t). In order to sample the pair of modulateddetection signals y₁(t) and y₂(t), two integrators 132 and 132′ areemployed to respectively integrate (or accumulate) the pair of modulateddetection signals y₁(t) and y₂(t) to generate two digital components I,Q of a two-dimensional detection vector. In this embodiment, the twointegrators 132 and 132′ are any proper integration circuits, such ascapacitors, without particular limitations. In addition to the twocontinuous signals mentioned above, the two mixing signals are selectedas two vectors, for example MX₁=[1 0 −1 0] and MX₂=[0 −1 0 1], so as tosimplify the circuit structure. The two mixing signals may be selectedfrom proper simplified vectors without particular limitations as long asthe process of modulation is simplified.

As the two digital components I and Q are accumulated values of the pairof modulated detection signals y₁(t) and y₂(t), the pair of modulateddetection signals y₁(t) and y₂(t) are sometimes directly referred to twodigital components of the two-dimensional detection vector herein. Asthe digital detection signal y_(d)(t) is a digitized value of thedetection signal y(t), the digital detection signal y_(d)(t) issometimes directly referred to the detection signal y(t) herein.

In FIG. 3B, the detection circuit 13 includes an analog-to-digitalconverter (ADC) 133, a mixer 131 and an integrator 132, and the twomixing signals MX₁ and MX₂ are inputted to the mixer 131 via amultiplexer 130 to be modulated with the digital detection signaly_(d)(t) so as to generate two modulated detection signals y₁(t) andy₂(t). In addition, functions of the ADC 133, the mixer 131 and theintegrator 132 are similar to those shown in FIG. 3A and thus detailsthereof are not repeated herein.

A detection method of the capacitive touch sensing device of the presentdisclosure includes the steps of: providing a drive signal to a firstelectrode of a sensing element; modulating a detection signal coupled toa second electrode from the drive signal through a coupling capacitancerespectively with two mixing signals so as to generate a pair ofmodulated detection signals; and calculating a scale of the pair ofmodulated detection signals to accordingly identify a touch event.

Referring to FIG. 3A or 3B for example, after the drive circuit 12provides a drive signal X(t) to the first electrode 101 of the sensingelement 10, the drive signal X(t) couples a detection signal y(t) on thesecond electrode 102 of the sensing element 10 through the couplingcapacitance 103. Next, the detection circuit 13 respectively modulates(or mixes) the detection signal y(t) with two mixing signals MX₁ and MX₂to generate a pair of modulated detection signals y₁(t) and y₂(t). Theprocessor 14 calculates a scale of the pair of modulated detectionsignals y₁(t) and y₂(t) to accordingly identify a touch event, whereinmethods of calculating a scale of the pair of modulated detectionsignals y₁(t) and y₂(t) as well as comparing the scale of the pair ofmodulated detection signals y₁(t) and y₂(t) with at least one thresholdmay be referred to FIG. 4 and its corresponding descriptions. Inaddition, before the scale of the pair of modulated detection signalsy₁(t) and y₂(t) is calculated, the integrator 132 and/or 132′ isoperable to accumulate the pair of modulated detection signals y₁(t) andy₂(t) to output two digital components I and Q of the two-dimensionaldetection vector (I,Q).

Referring to FIG. 5, it is a schematic diagram of a capacitive touchsystem according to one embodiment of the present disclosure, i.e. aplurality of capacitive touch sensing device being able to form acapacitive touch system. A plurality of sensing elements 10 arranged inmatrix forms a capacitive sensing matrix which is used as a touch panel.Each row of the sensing elements 10 is respectively driven by one ofdrive circuits 12 ₁-12 _(n) and the detection circuit 13 detects outputsignals y(t) of every column of the sensing elements 10 through aplurality of switch devices SW₁-SW_(m) or a multiplexer. As shown inFIG. 5, the drive circuit 12 ₁ is configured to drive a first row ofsensing elements 10 ₁₁-10 _(1m); the drive circuit 12 ₂ is configured todrive a second row of sensing elements 10 ₂₁-10 _(2m); . . . ; and thedrive circuit 12 _(n) is configured to drive an nth row of sensingelements 10 _(n1)-10 _(nm); wherein, n and m are positive integers andvalues thereof are determined according to the size and resolution ofthe capacitive sensing matrix without particular limitations.

In this embodiment, each of the sensing elements 10 (shown by circles 10₁₁ to 10 _(nm) herein) includes a first electrode and a second electrodeconfigured to form a coupling capacitance therebetween as shown in FIGS.2, 3A and 3B. The drive circuits 12 ₁-12 _(n) are respectively coupledto the first electrode of one row of the sensing elements 10. Forexample, a timing controller 11 is operable to control the drivecircuits 12 ₁-12 _(n) to respectively output a drive signal X(t) to thefirst electrode of the sensing elements 10. The drive circuits 12 ₁-12_(n) are configured to sequentially or concurrently drive the sensingelements 10 ₁₁ to 10 _(nm). It is appreciated that the drive circuits 12₁-12 _(n) in FIG. 5 may be integrated with the timing controller 11 toform a signal drive circuit.

The detection circuit 13 is coupled to the second electrode of onecolumn of the sensing elements 10 through a plurality of switch devicesSW₁-SW_(m) or a multiplexer to sequentially detect a detection signaly(t) coupled to the second electrode from the drive signal X(t) throughthe coupling capacitance of the sensing elements 10. The detectioncircuit 13 modulates the detection signal y(t) respectively with twomixing signals to generate a pair of modulated detection signals,wherein details of generating the pair of modulated detection signalshave been described in FIGS. 3A to 3B and their correspondingdescriptions and thus are not repeated herein.

The processor 14 identifies a touch event and a touch position accordingto the pair of modulated detection signals. As mentioned above, theprocessor 14 calculates a norm of vector of a two-dimensional detectionvector formed by the pair of modulated detection signals (e.g., I andQ), and identifies the touch event by comparing the norm of vector withat least one threshold TH as FIG. 4.

In an embodiment of sequential driving, when the timing controller 11controls the drive circuit 12 ₁ to output the drive signal X(t) to thefirst row of sensing elements 10 ₁₁-10 _(1m), the switch devicesSW₁-SW_(m) are sequentially conducted such that the detection circuit 13detects the detection signal y(t) sequentially outputted by everysensing element of the first row of sensing elements 10 ₁₁-10 _(1m),wherein the detection corresponding to each sensing element may bereferred to FIGS. 3A and 3B. Next, the timing controller 11 sequentiallycontrols other drive circuits 12 ₂-12 ₁₁ to output the drive signal X(t)to every row of the sensing elements. After the detection circuit 13detects all of the sensing elements 10 ₁₁ to 10 _(nm), a scan period ora frame period is accomplished. The processor 14 identifies theposition(s) of the sensing elements where a touch event occurs within ascan period as a touch position. It is appreciated that said touchposition may be occurred at more than one sensing elements 10, and theprocessor 14 takes all positions of the more than one sensing elements10 as touch positions or takes one of the positions (e.g., a center orgravity center) of the more than one sensing elements 10 as a touchposition.

In some embodiments, to save the power of the capacitive touch system inFIG. 5, the timing controller 11 controls at least a part of the drivecircuits 12 ₁-12 _(n) (more than one drive circuits) to concurrentlyoutput the drive signal X(t) to corresponded rows of the sensingelements. The detection circuit 13 modulates the detection signal y(t)of different columns with different two mixing signals MX₁ and MX₂,respectively. In addition, methods of identifying a touch event and atouch position are similar to FIG. 5, and thus details thereof are notrepeated herein. For example, different pairs of mixing signals MX₁ andMX₂ are previously stored in a non-volatile memory.

The detection circuit 13 may further include the filter and/or theamplifier to improve the signal quality. In addition, the processor 14may be combined with the detection circuit 13 to form a single element,and functions thereof are implemented by software and/or hardware.

The phase shift during signal transmission caused by capacitance onsignal lines may be ignored by calculating a norm of vector of atwo-dimensional detection vector. In other words, if a phase shiftexists between drive signals X(t) of every channel, the phase shift mayalso be ignored by calculating the norm of vector of the two-dimensionaldetection vector. Therefore, in an embodiment of concurrent driving, itis able to concurrently drive different input channels within the samedrive time slot using a plurality of drive signals having a phase shiftfrom each other, and to identify a touch event and/or a touch positionby calculating a norm of vector of two-dimensional detection vectors ofevery output channel in the detection end. In addition, it is able toeffectively use a dynamic range of ADC by phase-shifting drive signalsX(t) of different input channels, wherein the phase-shifting isimplemented by a random phase offset or a formulated phase offset, butnot limited thereto.

Referring to FIG. 7, it is a schematic diagram of a concurrent drivingcapacitive touch system 2 according to a first embodiment of the presentdisclosure. The capacitive touch system 2 includes a drive end 2T, acapacitive sensing matrix 200 and a detection end 2R, wherein thecapacitive sensing matrix 200 has a plurality of input channels and aplurality of output channels. For example, the capacitive sensing matrix200 includes a plurality of sensing elements (e.g., 20 ₁₁ to 20 _(nn))arranged in rows and columns, and said input channels herein arereferred to sensing element rows (or columns) driven by the drive end 2Tand said output channels herein are referred to sensing element columns(or rows) detected by the detection end 2R.

The drive end 2T is configured to concurrently input encoded andmodulated drive signals to a plurality of input channels (or a pluralityof drive electrodes D₁ to D_(n)) in each drive time slot of a pluralityof drive time slots of a scan period (or a frame period) of thecapacitive sensing matrix 200 in operation. The detection end 2R issequentially coupled to a plurality of output channels (or a pluralityof receiving electrodes S₁ to S_(n)) of the capacitive sensing matrix200 within the frame period, and configured to decode a plurality ofdetection matrices Md, which are obtained by detecting the outputchannels, so as to generate a two-dimensional detection vectorcorresponding to each of the sensing elements and calculate a norm ofvector of each of the two-dimensional detection vectors, wherein eachmatrix element of the detection matrices Md is a detection signalobtained corresponding to one receiving electrode in each of the drivetime slots and the detection matrices Md are one-dimensional matrices.The method of generating matrix elements of the detection matrices Md isreferred to FIGS. 3A and 3B. For example, the detection end 2R modulatesa plurality of detection signals y(t) of the receiving electrodes S₁ toS_(n) by two mixing signals M₁ and M₂ to respectively generate a pair ofmodulated detection signals y₁(t) and y₂(t), and accumulates the pair ofmodulated detection signals y₁(t) and y₂(t) by using the integrator torespectively generate a matrix element of the detection matrices Mdcorresponding to each pair of the modulated detection signals y₁(t) andy₂(t). The matrix elements associated with all drive time slots of theframe period form the detection matrices Md.

In addition, the detection end 2R further compares the norm of vectorswith at least one threshold so as to identify a touch event and/or atouch position (as shown in FIG. 4). In one aspect, a number of thedrive time slots is equal to a number of the input channels (or a numberof the drive electrodes D₁ to D_(n)).

In this embodiment, the encoded and modulated drive signals are encodedby using a Hadamard matrix, i.e. the drive end 2T encoding a drivesignal X(t) corresponding to each input channel by a Hadamard matrix.The detection end 2R decodes the detection matrix Md using an inverseHadamard matrix of the Hadamard matrix. The encoded and modulated drivesignals may only be phase modulated or may be phase and amplitudemodulated, e.g., using quadrature amplitude modulation (QAM).

In one embodiment, the capacitive touch system 2 includes a drivecircuit 22, an encoding module 25, a modulation module 26, thecapacitive sensing matrix 200, a detection circuit 23, a decoding module27 and a processor 24. In one embodiment, the drive circuit 22, theencoding module 25 and the modulation module 26 are combined to form thedrive end 2T; and the detection circuit 23, the decoding module 27 andthe processor 24 are combined to form the detection end 2R, wherein thedetection end 2R further includes an analog front end. It is appreciatedthat the drive end 2T and the detection end 2R may operatesynchronously.

In another embodiment, the encoding module 25 and the modulation module26 may be combined to form a single encoding and modulation module; andthe decoding module 27 may be integrated with the processor 24 or thedetection circuit 23.

The drive circuit 22 outputs a drive signal X(t) to the encoding module25, e.g., X(t)=Vd×exp(jwt), wherein Vd indicates a drive voltage value,w indicates a driving frequency and t indicates time. As describedabove, the drive signal X(t) is not limited to a continuous signal.

The encoding module 25 is configured to encode the drive signal X(t)corresponding to each row of the sensing elements (or each driveelectrode D₁ to D_(n)) so as to output a plurality of encoded drivesignals Xc(t). As mentioned above, the encoding module 25 encodes thedrive signal X(t) using an encoding matrix, e.g., a Hadamard matrix. Itis appreciated that as long as signals of every input channel aredistinguishable by encoding, other encoding matrices may be used. Inaddition, a size of the encoding matrix is determined by a number ofinput channels.

The modulation module 26 is configured to perform the phase modulationon the encoded drive signals Xc(t) corresponding to each row of thesensing elements (or each drive electrode D₁ to D_(n)) so as toconcurrently output encoded and modulated drive signals to each row ofthe sensing elements, and said phase modulation is to cause the encodedand modulated drive signals inputted into different rows of the sensingelements (or different drive electrodes D₁ to D_(n)) to have a phaseshift from each other. Accordingly, it is able to decrease an inputvoltage of the analog-to-digital (ADC) converter in the detection end 2R(as FIGS. 3A and 3B) so as not to exceed a dynamic range of the ADCconverter. In other embodiments, the encoded drive signals Xc(t) mayalso be amplitude and phase modulated, e.g., using quadrature amplitudemodulation. For example in FIG. 7, the modulation module 26 outputs anencoded and modulated drive signal X₁(t_(k)) to a first input channel,an encoded and modulated drive signal X₂(t_(k)) to a second inputchannel . . . and an encoded and modulated drive signal X_(n)(t_(k)) toan nth input channel, wherein k is referred to each drive time slot in ascan period herein, and X₁(t_(k)) to X_(n)(t_(k)) may be referred toFIG. 6.

For example, an encoding matrix may use equation (1) as an example andeach matrix element thereof is indicated by a_(rs), wherein thesubscript “r” of each matrix element a_(rs) is associated with eachdrive time slot (e.g. K₁ to K_(n)) and the subscript “s” of each matrixelement a_(rs) is associated with each input channel.

$\begin{matrix}\begin{bmatrix}a_{11} & a_{12} & \ldots & a_{1\; n} \\a_{21} & a_{22} & \ldots & a_{2\; n} \\\; & \; & \ddots & \; \\a_{n\; 1} & a_{n\; 2} & \ldots & a_{nn}\end{bmatrix} & (1)\end{matrix}$

The operation of the modulation module 26 may be representedmathematically by a diagonal matrix shown in equation (2), wherein x₁ tox_(n) are complex numbers and preferably have a phase shift from eachother. x₁ to x_(n) are configured to perform the phase modulation ondifferent input channels, respectively. When the quadrature amplitudemodulation (QAM) is used as a modulation mechanism, x₁ to x_(n) have anamplitude shift and a phase shift from each other, wherein the subscriptof x₁ to x_(n) is associated with each input channel.

$\begin{matrix}\begin{bmatrix}x_{1} & 0 & \ldots & 0 \\0 & x_{2} & \ldots & 0 \\\; & \; & \ddots & \; \\0 & 0 & \ldots & x_{n}\end{bmatrix} & (2)\end{matrix}$

Referring to FIGS. 6 and 7, based on equations (1) and (2), themodulation module 26 concurrently outputs a drive signal X(t)a₁₁x₁ tothe first input channel (or the drive electrode D₁), a drive signalX(t)a₁₂x₂ to the second input channel (or the drive electrode D₂) . . .and a drive signal X(t)a_(1n)x_(n) to the nth input channel (or thedrive electrode D_(n)) in a first drive time slot k=1; the modulationmodule 26 concurrently outputs a drive signal X(t)a₂₁x₁ to the firstinput channel, a drive signal X(t)a₂₂x₂ to the second input channel . .. and a drive signal X(t)a_(2n)x_(n) to the nth input channel in asecond drive time slot k=2; . . . and the modulation module 26concurrently outputs a drive signal X(t)a_(n1)x₁ to the first inputchannel, a drive signal X(t)a_(n2)x₂ to the second input channel . . .and a drive signal X(t)a_(nn)x_(n) to the nth input channel in an nthdrive time slot k=n. After the encoded and modulated drive signalsX₁(t_(k)) to X_(n)(t_(k)) of all time slots k=1 to k=n are inputted intothe capacitive sensing matrix 200, the operation of one drive frame (orframe period) is accomplished. In this embodiment, the drive time slotsK₁ to K_(n) are continuous in time or separated by a predetermined timeinterval from one another.

As mentioned above, the capacitive sensing matrix 200 includes a firstrow of sensing elements 20 ₁₁ to 20 _(1n), a second row of sensingelements 20 ₂₁ to 20 _(2n), . . . and an nth row of sensing elements 20_(n1) to 20 _(nn) (i.e. input channels 1 to n). The encoded andmodulated drive signals X(t)a₁₁x₁, X(t)a₁₂x₂, . . . X(t)a_(1n)x_(n) arerespectively inputted into the first row of sensing elements 20 ₁₁ to 20_(1n), the second row of sensing elements 20 ₂₁ to 20 _(2n), . . . andthe nth row of sensing elements 20 _(n1) to 20 _(nn) in the first drivetime slot k=1. The encoded and modulated drive signals inputted intoeach row of the sensing elements in other drive time slots k=2 to k=nare also shown in FIG. 6. In addition, signal lines of the capacitivesensing matrix 200 have different reactance with respect to drivesignals of different channels, and an one-dimensional matrix [y₁ y₂ . .. y_(n)]^(T) may be used to represent a reactance matrix of thecapacitive sensing matrix 200 mathematically. In one scan period, whenthe capacitive sensing matrix 200 is not touched, the reactance matrixis substantially unchanged; whereas when a touch occurs, at least onematrix element of the reactance matrix is changed such that thedetection signal y(t) is changed accordingly.

As shown in FIG. 7, each column of the sensing elements of thecapacitive sensing matrix 200 is coupled to the detection circuit 23 viaa respective switch device SW₁ to SW_(n) or a multiplexer. Within eachdrive time slot K₁ to K_(n) of one scan period, the switch devices SW₁to SW_(n) sequentially couple a corresponded column of the sensingelements to the detection circuit 23 to cause the detection circuit 23to couple to the capacitive sensing matrix 200 and generate a detectionmatrix Md corresponding to each column of the sensing elements accordingto a detection signal y(t) of each column of the sensing elements. Forexample FIG. 7 shows that the switch device SW₂ couples the secondcolumn of the sensing elements of the capacitive sensing matrix 200 tothe detection circuit 23 to generate a detection matrix Md correspondingto the second receiving electrode S₂.

The method of generating each matrix element (I₁+jQ₁) to (I_(n)+jQ_(n))of the detection matrix Md is, for example, referred to FIGS. 3A and 3B.For example, the detection circuit 23 modulates the detection signaly(t) of each drive time slot K₁ to K_(n) respectively with two mixingsignals MX₁ and MX₂ to generate a pair of modulated detection signalsy₁(t) and y₂(t), and accumulate the pair of modulated detection signalsy₁(t) and y₂(t) corresponding to each drive time slot K₁ to K_(n) by theintegrator (e.g., 132, 132′) to generate matrix elements of thedetection matrix Md. More specifically, the detection circuit 23respectively generates, within each drive time slot K₁ to K_(n), adetection signal, a pair of modulated detection signals and a matrixelement corresponding to one output channel, and the matrix elements ofall drive time slots K₁ to K_(n) form the detection matrix Md.

Therefore, after one scan period (i.e. one frame), the detection signaly(t) from every column of the sensing elements of the capacitive sensingmatrix 200 may be represented by X(t)×[encoding matrix]×[modulationmatrix]×[reactance matrix] as shown in equation (3) mathematically,wherein matrix elements of the encoding matrix are determined accordingto the encoding method being used; matrix elements of the modulationmatrix are determined according to the modulation mechanism being used;and matrix elements of the reactance matrix are determined according tothe capacitive sensing matrix 200. As mentioned above, the detectioncircuit 23 includes at least one integrator (as shown in FIGS. 3A and3B) configured to obtain two digital components, e.g., (I₁,Q₁) to(I_(n),Q_(n)) of the two-dimensional detection vector (HQ) according tothe detection signal y(t).

$\begin{matrix}{{y(t)} = {{x(t)} \times \begin{bmatrix}a_{11} & a_{12} & \ldots & a_{1\; n} \\a_{21} & a_{22} & \ldots & a_{2\; n} \\\; & \; & \ddots & \; \\a_{n\; 1} & a_{n\; 2} & \ldots & a_{nn}\end{bmatrix} \times \begin{bmatrix}x_{1} & 0 & \ldots & 0 \\0 & x_{2} & \ldots & 0 \\\; & \; & \ddots & \; \\0 & 0 & \ldots & x_{n}\end{bmatrix} \times \begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{n}\end{bmatrix}}} & (3)\end{matrix}$

Therefore, detection vectors corresponding to each column of the sensingelements outputted by the detection circuit 23 after one scan period maybe represented by a detection matrix Md=[(I₁+jQ₁) (I₂+jQ₂)(I_(n)+jQ_(n))]^(T), wherein (I₁+jQ₁) is the detection vector obtainedaccording to a detection signal y(t) of one column (e.g. the secondcolumn) of the sensing elements in the first drive time slot k=1. As theencoded and modulated drive signals X₁(t_(k)) to X_(n)(t_(k)) arerespectively inputted into every input channel in the first drive timeslot k=1, the detection vector (I₁+jQ₁) contains the superposition ofdetection signals associated with all input channels in the first drivetime slot k=1 and is a superposed detection vector. Similarly, (I₂+jQ₂)is the detection vector obtained according to the detection signal y(t)of one column of the sensing elements in the second drive time slot k=2and is a superposed detection vector of detection signals associatedwith all input channels in the second drive time slot k=2; . . . ;(I_(n)+jQ_(n)) is the detection vector obtained according to thedetection signal y(t) of one column of the sensing elements in the nthdrive time slot k=n and is a superposed detection vector of detectionsignals associated with all input channels in the nth drive time slotk=n. More specifically, each of the matrix elements (I₁+jQ₁) to(I_(n)+jQ_(n)) of the detection matrix Md is a superposed detectionvector.

For decoupling the superposed detection vectors associated witheveryinput channel, the detection circuit 23 sends the detection matrix Md tothe decoding module 27 for decoding thereby respectively generate atwo-dimensional detection vector corresponding to every sensing element(e.g. 20 ₁₁ to 20 _(nn)). For example, the decoding module 27 outputstwo-dimensional detection vectors of every input channel (i.e. thesensing element) in one column (e.g., the second column) of the sensingelements as shown by equation (4), wherein the two-dimensional detectionvector corresponding to input channel 1 of the second column of thesensing elements is represented by (i₁₂+jq₁₂), the two-dimensionaldetection vector corresponding to input channel 2 of the second columnof the sensing elements is represented by (i₂₂+jq₂₂), . . . and thetwo-dimensional detection vector corresponding to input channel n of thesecond column of the sensing elements is represented by(i_(n2)+jq_(n2)), wherein i and q are two digital components of thetwo-dimensional detection vectors, and (i₁₂+jq₁₂) to (i_(n2)+jq_(n2))are decoupled two-dimensional detection vectors. In FIG. 7, after onescan period, the decoding module 27 may output a set of two-dimensionaldetection vectors (i+jq) corresponding to every column of the sensingelements (or every receiving electrode); i.e. n sets of decoupledtwo-dimensional detection vectors [(i₁+jq₁) (i₂+jq₂) . . .(i_(n)+jq_(n))]^(T) and each two-dimensional detection vectorcorresponds to one sensing element. The decoding module 27 may use aninverse matrix of the encoding matrix, e.g., using an inverse matrix ofthe Hadamard matrix, to decode the superposed detection vectors (i.e.the detection matrices) to decouple the superposed detection vectors.

$\begin{matrix}{\begin{bmatrix}{i_{1} + {jq}_{1}} \\{i_{2} + {jq}_{2}} \\\vdots \\{i_{n} + {jq}_{n}}\end{bmatrix} = {\begin{bmatrix}{I_{1} + {jQ}_{1}} \\{I_{2} + {jQ}_{2}} \\\vdots \\{I_{n} + {jQ}_{n}}\end{bmatrix}\begin{bmatrix}a_{11} & a_{12} & \ldots & a_{1\; n} \\a_{21} & a_{22} & \ldots & a_{2\; n} \\\; & \; & \ddots & \; \\a_{n\; 1} & a_{n\; 2} & \ldots & a_{nn}\end{bmatrix}}^{T}} & (4)\end{matrix}$

Finally, the processor 24 calculates a norm of vector of each of thetwo-dimensional detection vectors, e.g., (i₁₁+jq₁₁) to (i_(nn)+jq_(nn)),and compares the obtained norm of vectors with at least one threshold THto confirm a touch as shown in FIG. 4.

Accordingly, after one scan period, the processor 24 identifies a touchevent and/or a touch position on the capacitive sensing matrix 200according to comparison results of comparing n×n norm of vectors withthe threshold TH, wherein n is a size of the capacitive sensing matrix.

In addition, when the drive signal X(t) is also amplitude modulated inthis embodiment, the processor 24 may further include an automatic levelcontrol (ALC) to eliminate the amplitude shift. For example, the controlparameter of the ALC when the capacitive sensing matrix 200 is nottouched is previously stored in the processor 24 (or an additionalmemory) to allow detection results of every sensing element to besubstantially identical. Accordingly, when a touch occurs, it is able toidentify the touch event more accurately.

In addition, as mentioned above, each of the sensing elements (20 ₁₁ to20 _(nn)) includes a first electrode 101 and a second electrode 102configured to form a coupling capacitance 103 (as shown in FIGS. 2, 3Aand 3B). The encoded and modulated drive signals X₁(t_(k)) toX_(n)(t_(k)) are coupled to the first electrode 101. The detectioncircuit 23 is coupled to the second electrode 102 and configured todetect a detection signal y(t) coupled to the second electrode 102 fromthe encoded and modulated drive signals X₁(t_(k)) to X_(n)(t_(k))through the coupling capacitance 103.

Referring to FIGS. 8 and 9, FIG. 8 is a schematic block diagram of adrive end 2T of a capacitive touch system according to a secondembodiment of the present disclosure; and FIG. 9 is a schematic blockdiagram of a detection end 2R of a capacitive touch system according toa second embodiment of the present disclosure. The capacitive touchsystem of this embodiment also includes a capacitive sensing matrix 200,a drive end 2T and a detection end 2R, and is different from FIG. 7 inthat the modulation module 26 further generates a drive signalcontaining a plurality of driving frequencies to drive the capacitivesensing matrix 200. In addition, the modulation module 26 is still ableto perform the phase modulation on the encoded drive signals Xc(t)corresponding to each row of the sensing elements as the above firstembodiment such that the encoded and modulated drive signalscorresponding to different rows of the sensing elements have a phasedifference from each other to improve the dynamic detection range.

The capacitive sensing matrix 200 also includes a plurality of driveelectrodes D₁-D_(n) and a plurality of receiving electrodes S₁-S_(n) toform a plurality of sensing elements 20 ₁₁-20 _(nn) arranged in rows andcolumns as shown in FIG. 7. In FIG. 8, the encoding module 25 is shownto include encoders 251-25 n configured to respectively encode a drivesignal X(t) outputted by the drive circuit 22, and it is only intendedto illustrate but not to limit the present disclosure. The encodingmodule 25 is configured to encode the drive signal X(t) corresponding toeach row of the sensing elements to output a plurality of encoded drivesignals Xc(t), and the encoding method has been illustrated above andthus details thereof are not repeated herein.

In this embodiment, the modulation module 26 modulates the encoded drivesignals Xc(t) using frequency division multiplexing (FDM) toconcurrently output a plurality of encoded and modulated drive signalsX₁-X_(n) to each row of the sensing elements (or drive electrodesD₁-D_(n)), wherein each of the encoded and modulated drive signalsX₁-X_(n) contains a plurality of driving frequencies f₁-f_(N). Themodulation module 26 modulates the encoded drive signals Xc(t) usingconventional frequency division multiplexing or orthogonal frequencydivision multiplexing (OFDM) as shown in FIG. 10. For example, FIG. 8shows that a plurality of driving frequencies f₁-f_(N) are used tomodulate the drive signal Xc(t) and the signal mixing is performed togenerate the encoded and modulated drive signals X₁-X_(n). In someembodiments, a frequency difference between the driving frequenciesf₁-f_(N) is selected between 50 KHZ to 150 KHZ, but not limited thereto.A number of the driving frequencies f₁-f_(N) is not particularly limitedand is determined according to the frequency difference and an operablefrequency range.

In FIG. 9, the detection end 2R is shown to include an analog front end2 af, a multiplexer 2 am and a digital back end 2 db. The analog frontend 2 af is used to, for example, convert current signals to voltagesignals and to filter the voltage signals using an analog filter toincrease the signal to noise ratio and output a detection signal y(t).In other words, in this embodiment the detection signal y(t) is avoltage signal. The multiplexer 2 am is used to, for example, couple thedetection signals y(t) of different receiving electrodes S₁-S_(n) to ananalog to digital converter 133 for digitization, wherein the functionof the multiplexer 2 am is similar to the switch devices SW₁ to SW_(n)of FIG. 7. In some embodiments, the analog to digital converter 133digitizes the detection signal y(t) using an oversampling to generate adigital detection signal y_(d)(t). In FIG. 9, although the analog todigital converter 133 is shown to be included in the detection circuit23, it is only intended to illustrate but not to limit the presentdisclosure as long as the analog to digital converter 133 is coupledbetween the capacitive sensing matrix 200 and the detection circuit 23.

The detection circuit 23 is electrically coupled to the capacitivesensing matrix 200 and configured to respectively generate a detectionmatrix Md corresponding to each of the driving frequencies f₁-f_(N)according to a detection signal y(t) of each column of the sensingelements. For example, corresponding to each receiving electrodeS₁-S_(n), the detection circuit 23 generates a detection matrixMd_f₁=[I₁ _(_) _(f1)+jQ₁ _(_) _(f1) . . . I_(n) _(_) _(f1)+jQ_(n) _(_)_(f1)]^(T) corresponding to the driving frequency f₁; generates adetection matrix Md_f₂=[I₁ _(_) _(f2)+jQ₁ _(_) _(f2) . . . I_(n) _(_)_(f2)+jQ_(n) _(_) _(f2)]^(T) corresponding to the driving frequency f₂;. . . and generates a detection matrix Md_f_(N)=[I₁ _(_) _(fN)+jQ₁ _(_)_(fN) . . . I_(n) _(_) _(fN)+jQ_(n) _(_) _(fN)]^(T) corresponding to thedriving frequency f_(N). In some embodiments, the detection circuit 23includes at most 2N mixers 131, 131′ and N bandpass filters, wherein Nis a number of the driving frequencies f₁-f_(N). It is appreciated thatif all driving frequencies f₁-f_(N) are not used together, an effectivenumber of N is not fixed.

As mentioned above, a pair of mixers 131, 131′ are used to modulate thedetection signal, e.g., the digital detection signal y_(d)(t), using twomixing signals MX₁ and MX₂ to generate a pair of modulated detectionsignals y₁(t) and y₂(t). The bandpass filters are used to filter thepair of modulated detection signals y₁(t) and y₂(t) to respectivelygenerate every matrix element of a detection matrix Md corresponding toeach of the driving frequencies f₁-f_(N).

As mentioned above, if a concurrent driving mode is adopted, everymatrix element of the detection matrix Md is a superposed detectionvector which needs to be decoupled by the decoding module 27. If theconcurrent driving mode is not adopted, each matrix element of thedetection matrix Md is a two-dimensional detection vector correspondingto one sensing element.

More specifically, as the drive signals X₁(tk)-X_(n)(tk) provided toeach row of the sensing elements in FIG. 7 contain a single frequency, asingle detection matrix Md is generated corresponding to each column ofthe sensing elements (or receiving electrodes S₁-S_(n)). In FIG. 9, asthe drive signals X₁-X_(n) provided to each row of the sensing elementsis a mixed signal containing a plurality of driving frequenciesf₁-f_(N), the detection circuit 23 respectively generate one detectionmatrix Md corresponding to each of the driving frequencies f₁-f_(N)corresponding to each column of the sensing elements (or receivingelectrodes S₁-S_(n)). Accordingly, when some frequencies are interferedby noises, those driving frequencies among the driving frequenciesf₁-f_(N) having better signal quality are directly selected in thefollowing touch identification without using so-called frequency hoppingwhich sequentially drives the capacitive sensing matrix 200 in order toselect a proper driving frequency. In some embodiments, when the analogto digital converter 133 samples the detection signal y(t) using anoversampling, the detection circuit 23 further includes downconversionunits 134 and 134′ to perform a downconversion on the pair of modulateddetection signals y₁(t) and y₂(t), and a ratio of the downconversion isdetermined according to a multiple of the oversampling.

The decoding module 27 decodes the detection matrices Md_f₁ to Md_f_(N)to output a plurality of two-dimensional detection vectors correspondingto each of the sensing units (e.g., 20 ₁₁-20 _(nn) shown in FIG. 7),wherein the plurality of two-dimensional detection vectors associatedwith each of the sensing elements respectively correspond to the drivingfrequencies f₁-f_(N). More specifically, the decoding module 27 obtainsa plurality of two-dimensional detection vectors i₁₁+iq₁₁ correspondingto the sensing elements 20 ₁₁, and each two-dimensional detection vectori₁₁+iq₁₁ corresponds to one of the driving frequencies f₁-f_(N).Similarly, the decoding module 27 respectively obtains a plurality oftwo-dimensional detection vectors i₁₂+iq₁₂ to corresponding to thesensing elements 20 ₁₂-20 _(nn). Accordingly, the processor 24respectively calculates norm of vectors of n×n two-dimensional detectionvectors corresponding to each of the driving frequencies f₁-f_(N), i.e.N×n×n norm of vectors.

More specifically, in the above first embodiment, the drive signal ofthe drive end 2T for driving each of the input channels substantiallycontains a single driving frequency, and thus the detection end 2Rgenerates one two-dimensional detection vector and a norm of vectorthereof corresponding to each sensing element within every frame period.In the second embodiment, the drive signal of the drive end 2T fordriving each of the input channels contains a plurality of drivingfrequencies, and thus the detection end 2R generates a plurality oftwo-dimensional detection vectors and norm of vectors thereofcorresponding to each sensing element within every frame period, whereinthe two-dimensional detection vectors and norm of vectors respectivelycorrespond to the driving frequencies f₁-f_(N). The method of generatingeach two-dimensional vector and norm of vector in the second embodimentis similar to that of the first embodiment, only the second embodimentfurther including the steps of mixing and extracting signals ofdifferent driving frequencies.

It should be mentioned that the single driving frequency mentioned inthis embodiment is referred to a predetermined operating frequencybetween the drive end 2R and the detection end 2T. In some conditions,the drive signal may be interfered by noises to contain other frequencysignals. In the present disclosure, said driving frequency does notinclude the noise frequency.

Referring to FIG. 11, it is a flow chart of an operating method of acapacitive touch system according to a second embodiment of the presentdisclosure which includes the steps of: concurrently inputting encodedand modulated drive signals X₁-X_(n) to the drive electrodes D₁-D_(n) ineach drive time slot of a plurality of drive time slots of a frameperiod of the capacitive sensing matrix 200, wherein the encoded andmodulated drive signals X₁-X_(n) are modulated by frequency divisionmultiplexing (FDM) to contain a plurality of driving frequenciesf₁-f_(N) (Step S31); sequentially detecting the receiving electrodesS₁-S_(n) of the capacitive sensing matrix 200 within the frame period torespectively generate a plurality of detection matrices Md correspondingto each of the receiving electrodes S₁-S_(n), wherein the detectionmatrices Md associated with each of the receiving electrodes S₁-S_(n)respectively correspond to the driving frequencies f₁-f_(N) (Step S32);and decoding the detection matrices Md to generate a plurality oftwo-dimensional detection vectors corresponding to each of the drivingfrequencies f₁-f_(N) of each of the receiving electrodes S₁-S_(n) (StepS33). Details of this operating method has been illustrated above, e.g.,the Step S31 being performed by the drive end 2T, and the Steps S32-S33being performed by the detection end 2R, and thus details thereof arenot repeated herein.

As mentioned above, the detection end 2R modulates a plurality ofdetection signals y(t) obtained by detecting the receiving electrodesS₁-S_(n) using two mixing signals MX₁ and MX₂ to respectively generate apair of modulated detection signals y₁(t) and y₂(t). The detection end2R further filters the pair of modulated detection signals y₁(t) andy₂(t) using a digital filter (e.g., a bandpass filter) to respectivelygenerate the detection matrices Md_f₁ to Md_f_(N) corresponding to thedriving frequencies f₁-f_(N) as shown in FIG. 9. As mentioned above,before decoding, the matrix elements of the detection matrices may beintegrated or accumulated at first.

In some embodiments, the detection end 2R further uses downconversionunits 134, 134′ to perform a downconversion on the pair of modulateddetection signals y₁(t) and y₂(t), and a ratio of the downconversion isdetermined according to a multiple of the oversampling performed by theanalog to digital converter 133.

Finally, the detection end 2R calculates norm of vectors of a pluralityof two-dimensional detection vectors corresponding to each of thesensing elements (e.g., 20 ₁₁-20 _(nn), shown in FIG. 7), wherein eachof the plurality of two-dimensional detection vectors corresponding toeach of the sensing elements 20 ₁₁-20 _(nn) corresponds to one of thedriving frequencies f₁-f_(N). The detection end 2R compares the norm ofvectors with at least one threshold to identify a touch as shown in FIG.4.

Accordingly, the capacitive touch system of the second embodiment of thepresent disclosure is able to detect detection results of a plurality ofdriving frequencies f₁-f_(N) within one frame period to directly selectthe detection result of those driving frequencies having better signalquality to be outputted or to compare the detection results of everydriving frequencies to confirm the touch state thereby improving theidentification accuracy and reducing the power consumption and detectiontime interval.

It should be mentioned that although the above embodiments take themutual capacitive touch system as an example for illustration, thepresent disclosure is not limited thereto. More specifically, thecapacitive touch system of the present disclosure is applicable to boththe self and mutual capacitive touch systems as long as mixed signalsinputted into each input channel contain a plurality of drivingfrequencies f₁-f_(N). The detection circuit respectively generates atwo-dimensional detection vector corresponding to each of the drivingfrequencies f₁-f_(N) and corresponding to each sensing element. Theprocessor 24 selects the driving frequency having an optimum signal tonoise ratio among the two-dimensional detection vectors corresponding toeach sensing element to achieve the object of eliminating the noiseinterference. The processor 24 may further calculate an average, asummation or a weighted summation of the plurality of two-dimensionaldetection vectors corresponding to different driving frequenciesassociated with every sensing element to improve the identificationaccuracy.

It should be mentioned that although the above first and secondembodiments are illustrated by concurrent driving, it is only intendedto illustrate but not to limit the present disclosure. In the embodimentof the sequential driving, e.g., the drive circuit 22 sequentiallydriving the input channels (e.g., drive electrodes D₁-D_(n)), theencoding module 25 and the decoding module 26 are not implemented, andthe detection end 2R sequentially generates a two-dimensional detectionvector corresponding to each of the driving frequencies f₁-f_(N)associated with each of the sensing elements 10 ₁₁-10 _(nn). Thedetection end 2 is not necessary to generate the detection matrix Md asshown in FIG. 7 at first and then generate the two-dimensional detectionvector by decoding. In the embodiment of the sequential driving, thedetection end 2R still generates a plurality of two-dimensionaldetection vectors corresponding to each sensing element.

In this embodiment, the drive circuit 22 sequentially inputs a drivesignal X(t) to each row of the sensing elements (or drive electrodesD₁-D_(n)), and the detection circuit 23 sequentially detects each columnof the sensing elements (or receiving electrodes S₁-S_(n)) through themultiplexer 2 am (or a plurality of switch devices SW₁-SW_(n)). As theencoding is not performed, the modulation module 26 modulates the drivesignal X(t) using frequency division multiplexing to respectively outputa modulated drive signal X₁-X_(n) to each row of the sensing elements.Similarly, in this embodiment, each of the modulated drive signalsX₁-X_(n) contains a plurality of driving frequencies f₁-f_(N) as shownin FIG. 10.

As the decoding is not performed, the detection circuit 23 is coupled tothe capacitive sensing matrix 200 to respectively generate atwo-dimensional detection vector corresponding to each of the drivingfrequencies f₁-f_(N) according to a detection signal y(t) of each columnof the sensing elements. As the drive end 2R sequentially drives eachrow of the sensing elements and the detection end 2T sequentiallydetects each column of the sensing elements, the above detection signaly(t) of each column of the sensing elements is associated with thedetection result of one sensing element. Accordingly, the detectioncircuit 23 is able to directly output at most N (i.e. a number ofdriving frequencies) two-dimensional detection vectors corresponding toeach sensing element.

In this embodiment, the detection circuit 23 modulates the detectionsignal y(t) using two mixing signals MX₁ and MX₂ to generate a pair ofmodulated detection signals y₁(t) and y₂(t), and filters the pair ofmodulated detection signals y₁(t) and y₂(t) to respectively generate atwo-dimensional detection vector corresponding to each of the drivingfrequencies f₁-f_(N) associated with each sensing element. As mentionedabove, according to an oversampling frequency of the analog to digitalconverter 133, the detection circuit 23 further performs adownconversion on the pair of modulated detection signals y₁(t) andy₂(t).

In some embodiments, under different conditions (e.g., some frequencieshaving larger noises), it is possible that the capacitive touch systemselects different driving frequencies to perform the driving withoutusing all driving frequencies at the same time, e.g., comparingtwo-dimensional detection vectors corresponding to different drivingfrequencies to determine the better driving frequencies or drivingfrequencies not being used.

The capacitive touch system of the present disclosure includes a controlchip and the capacitive sensing matrix 200, which is coupled to thecontrol chip via the drive electrodes D₁-D_(n) and the receivingelectrodes S₁-S_(n). The control chip includes the drive end 2T and thedetection end 2R. In other words, the above driving the capacitivesensing matrix 200, receiving the detection signal y(t), mixing thedetection signal y(t) using two mixing signal to generate a pair ofmodulated detection signals y₁(t) and y₂(t), calculating the norm ofvector and identifying a touch may all be performed by the control chip.

In addition, as mentioned above, to increase a dynamic range of theanalog-to-digital converter, in the second embodiment a phase shift isarranged between the drive signals of different input channels. In otherwords, it is possible to combine the first and second embodiments suchthat the drive signals of each input channel contain a plurality ofdriving frequencies and the drive signals between different inputchannels have a phase shift from each other.

In addition, although the above embodiment takes the capacitive sensingmatrix 200 as an example for illustration, the present disclosure is notlimited thereto. In other embodiments, the capacitive touch system ofthe present disclosure is also applicable to a capacitive touch sensingdevice including a single sensing element 10 (as the capacitive touchsensing device shown in FIG. 0.2). For example, the capacitive touchsensing device is used as a switching device to control the ON/OFF of anelectronic device. In addition, it is possible that the capacitive touchsensing device includes more than one sensing element 10, and the morethan one sensing elements 10 are not necessary to be arranged in amatrix. When the capacitive touch sensing device includes a plurality ofsensing elements 10 arranged in rows and columns, a capacitive sensingmatrix 200 is formed.

Accordingly, in this embodiment the capacitive touch sensing deviceincludes an input channel coupled to the drive circuit 22 and an outputchannel coupled to the analog front end 2 af and the digital backend 2db. If a single sensing element 10 is included, the multiplexer 2 am maynot be implemented.

The capacitive touch system of this embodiment includes a drive circuit,a capacitive touch sensing device, a modulation module and a detectioncircuit, wherein the capacitive touch sensing device includes, forexample, a single sensing element or a plurality of sensing elementswhich form a single equivalent capacitor (self or mutual capacitor). Thedrive circuit outputs a drive signal, wherein the drive signal is usedto drive the single sensing element or the single equivalent capacitor.The capacitive touch sensing device includes at least one sensingelement. The modulation module is used to modulate the drive signalusing frequency division multiplexing to output a modulated drive signalto the at least one sensing element, wherein the modulated drive signalcontains a plurality of driving frequencies (as shown in FIG. 10). Thedetection circuit is coupled to the capacitive touch sensing device andused to respectively generate a two-dimensional detection vectorcorresponding to each of the driving frequencies according to adetection signal from the at least one sensing element.

In this embodiment, the capacitive touch sensing device of thecapacitive touch system is also used to detect a capacitance variationto identify whether an object approaches or touches the capacitive touchsensing device. The operating method of this embodiment is similar tothe previous embodiment, and the difference is that the drive circuit 22drives at least one sensing element and the detection circuit 23 detectsa detection signal y(t) of the at least one sensing element. Thepost-processing performed by the digital backend 2 db on the detectionsignal y(t) has been illustrated above, and thus details thereof are notrepeated herein.

As mentioned above, when capacitive sensors are applied to differentelectronic devices, they are interfered by noises of the electronicdevices to degrade the detection accuracy. Therefore, the presentdisclosure further provides a capacitive touch system (FIGS. 7-9) and anoperating method thereof (FIG. 11) that input a mixed signal containinga plurality of driving frequencies into each input channel modulated byfrequency division multiplexing to overcome the noise interference andimprove the detection accuracy as well as reducing the power consumptionand shortening the detection time interval.

Although the disclosure has been explained in relation to its preferredembodiment, it is not used to limit the disclosure. It is to beunderstood that many other possible modifications and variations can bemade by those skilled in the art without departing from the spirit andscope of the disclosure as hereinafter claimed.

What is claimed is:
 1. A capacitive touch system comprising: a drive circuit configured to output a drive signal; a capacitive sensing matrix comprising a plurality of sensing elements arranged in rows and columns; an encoding module configured to encode the drive signal corresponding to each row of the sensing elements to output a plurality of encoded drive signals; a modulation module configured to modulate the encoded drive signals using frequency division multiplexing and concurrently output encoded and modulated drive signals to each row of the sensing elements, wherein each of the encoded and modulated drive signals contains a plurality of driving frequencies; a detection circuit coupled to the capacitive sensing matrix and configured to respectively generate a detection matrix corresponding to each of the driving frequencies according to a detection signal of each column of the sensing elements; and a decoding module configured to decode the detection matrices to output a plurality of two-dimensional detection vectors corresponding to each of the sensing elements, wherein the two-dimensional detection vectors associated with each of the sensing elements respectively correspond to the driving frequencies.
 2. The capacitive touch system as claimed in claim 1, wherein the detection circuit is configured to modulate the detection signal with two mixing signals to generate a pair of modulated detection signals; and filter the pair of modulated detection signals to respectively generate the detection matrix corresponding to each of the driving frequencies.
 3. The capacitive touch system as claimed in claim 2, wherein the detection circuit is further configured to perform a downconversion on the pair of modulated detection signals.
 4. The capacitive touch system as claimed in claim 3, further comprising an analog to digital converter coupled between the capacitive sensing matrix and the detection circuit, and configured to digitize the detection signal using an oversampling.
 5. The capacitive touch system as claimed in claim 1, further comprising a processor configured to respectively calculate a norm of vector of the two-dimensional detection vectors.
 6. The capacitive touch system as claimed in claim 1, wherein the modulation module is further configured to phase-modulate the encoded drive signals corresponding to each row of the sensing elements to cause the encoded and modulated drive signals corresponding to different rows of the sensing elements to have a phase difference therebetween.
 7. The capacitive touch system as claimed in claim 1, wherein the encoding module is configured to encode the drive signal with a Hadamard matrix, and the decoding module is configured to decode the detection matrices with an inverse matrix of the Hadamard matrix.
 8. The capacitive touch system as claimed in claim 1, wherein the frequency division multiplexing is orthogonal frequency division multiplexing.
 9. The capacitive touch system as claimed in claim 1, wherein a frequency difference between the driving frequencies is 50 KHZ to 150 KHZ.
 10. An operating method of a capacitive touch system, the capacitive touch system comprising a capacitive sensing matrix which comprises a plurality of drive electrodes and a plurality of receiving electrodes, the operating method comprising: concurrently inputting encoded and modulated drive signals to the drive electrodes in each drive time slot of a plurality of drive time slots of a frame period of the capacitive sensing matrix, wherein the encoded and modulated drive signals are modulated by frequency division multiplexing to contain a plurality of driving frequencies; sequentially detecting the receiving electrodes of the capacitive sensing matrix within the frame period to generate a plurality of detection matrices corresponding to each of the receiving electrodes, wherein the detection matrices associated with each of the receiving electrodes respectively correspond to the driving frequencies; and decoding the detection matrices to generate a plurality of two-dimensional detection vectors corresponding to each of the driving frequencies of each of the receiving electrodes.
 11. The operating method as claimed in claim 10, further comprising: modulating a plurality of detection signals generated by detecting the receiving electrodes using two mixing signals to respectively generate a pair of modulated detection signals; and filtering the pair of modulated detection signals to respectively generate the detection matrices corresponding to the driving frequencies.
 12. The operating method as claimed in claim 10, further comprising: performing a downconversion on the pair of modulated detection signals.
 13. The operating method as claimed in claim 10, further comprising: calculating norm of vectors of the two-dimensional detection vectors; and comparing the norm of vectors with at least on threshold to identify a touch.
 14. The operating method as claimed in claim 10, wherein the encoded and modulated drive signals corresponding to different drive electrodes have a phase difference therebetween.
 15. The operating method as claimed in claim 10, further comprising: comparing the two-dimensional detection vectors of different driving frequencies to determine an optimum driving frequency.
 16. A capacitive touch system comprising: a drive circuit configured to output a drive signal; a capacitive touch sensing device comprising at least one sensing element; a modulation module configured to modulate the drive signal using frequency division multiplexing and output a modulated drive signal to the at least one sensing element, wherein the modulated drive signal contains a plurality of driving frequencies; and a detection circuit coupled to the capacitive touch sensing device and configured to respectively generate a two-dimensional detection vector corresponding to each of the driving frequencies according to a detection signal of the at least one sensing element.
 17. The capacitive touch system as claimed in claim 16, wherein the capacitive touch sensing device is a capacitive sensing matrix which comprises a plurality of sensing elements arranged in rows and columns, the modulation module is configured to respectively output a modulated drive signal to each row of the sensing elements, and the detection circuit is configured to respectively generate the two-dimensional detection vector corresponding to each of the driving frequencies according to a detection signal of each column of the sensing elements.
 18. The capacitive touch system as claimed in claim 17, wherein the detection circuit is configured to modulate the detection signal with two mixing signals to generate a pair of modulated detection signals; and filter the pair of modulated detection signals to respectively generate the two-dimensional detection vector corresponding to each of the driving frequencies.
 19. The capacitive touch system as claimed in claim 18, wherein the detection circuit is further configured to perform a downconversion on the pair of modulated detection signals.
 20. The capacitive touch system as claimed in claim 19, further comprising an analog to digital converter coupled between the capacitive sensing matrix and the detection circuit, and configured to digitize the detection signal using an oversampling.
 21. The capacitive touch system as claimed in claim 16, further comprising a processor configured to calculate a norm of vector of the two-dimensional detection vector. 